The composition and metabolism of high density lipoprotein subfractions

The composition and metabolism of high density lipoprotein (HDL) subfractions were investigated in seven nomal individuals. Mean HDL₂ (d, 1.063–1.125 g/ml) composition (by weight) was 43% protein, 28% phospholipid, 23% cholesterol, and 6% triglyceride, and mean HDL₃ (d, 1.125–1.21 g/ml) composition was 58% protein, 22% phospholipid, 14% cholesterol, and 5% triglyceride. The mean apoA-I; apoA-II weight ratio was 4.75 for HDL₂ and 3.65 for HDL₃.HDL₂ protein was proportionally slightly richer in C apolipoproteins and higher molecular weight constituents (including apoE) than HDL₃. Kinetic studies utilizing radiolabeled HDL_A (d, 1.09–1.21 g/ml), HDL₂, and HDL₃ demonstrated rapid exchange of apoA-I and apoA-II radioactivity among HDL subfractions, similar fractional rates of catabolism of apoA-I and apoA-II within HDL, and similar radioactivity decay within HDL subfractions. Mean plasma residence time was 5.74 days for radiolabeled HDL₂ and 5.70 days for radiolabeled HDL₃. Differences in HDL protein mass among individuals were largely due to alterations in catabolism, and in general both HDL₂ and HDL₃ were catabolized via a plasma and a nonplasma pathway. Data from simultaneous radiolabeled very low density lipoprotein and HDL studies in 2 individuals are consistent with the concept that apoC-II and apoC-III are catabolized at a different rate than are apoA-I and apoA-II within the HDL density range.     

The distribution of serum high density lipoprotein subfractions in non-human primates

The ultracentrifugal flotation patterns in 1.2 g/ml solvent and ultracentrifugal gradient distribution of high density lipoproteins (HDL) from the primates-human, apes and monkeys-were determined, with emphasis on the gorilla species of apes and rhesus monkeys. Diets for non-human primates were commercial chow, which is low in cholesterol. Molecular weights and protein, cholesterol, phospholipid and triglyceride compositions of various density fractions were determined on human, gorilla and rhesus HDL. The HDL₂/HDL₃ ratio was determined from the two peaks observed upon flotation in high salt in the analytical ultracentrifuge. The HDL₂ of all three species of apes-gorillas (Gorilla gorilla), chimpanzees (Pan troglodytes) and orangutans (Pongo pygmaeus)—was always greater than HDL₃, while that of all six species of Old World monkeys-Rhesus (Macaca mulatta), sooty mangabeys (Cercocebus atys), cynomolgus (Macaca fascicularis), stumptails, (Macaca arctoides) patas (Erythrocebus patas) and African greens (Cercopithecus aethiops)—was less. In addition, the HDL₃ concentration in five gorillas was about 15 mg/dl as cholesterol while the HDL₂ concentration was 92 mg/dl, much lower and higher, respectively, than humans. HDL₂ of gorillas was similar in density and molecular weight to that of humans. The distribution of densities in gorilla HDL was predominantly in HDL₂, while rhesus HDL usually, but not always, was unimodal, having a density distribution similar in heterogeneity to human HDL₃, but somewhat less dense (peaking at 1.109 vs 1.129 g/ml). The molecular weight of rhesus HDL was about the same as human HDL₃ in all three density subfractions and at the peak density. Likewise, the chemical compositions were similar for the subfractions 1.10–1.125 and>1.125 g/ml for rhesus HDL and human HDL₃. Consequently most but not all chow-fed rhesus HDL was very similar to human HDL₃, but lighter in density. A preliminary report of this study was given at the American Society for Biological Chemists Meeting in New Oreleans in April 1982.     

Human low density lipoprotein structure: Correlations with serum lipoprotein concentrations

Human low density lipoproteins (LDL) were isolated and purified from individuals having widely differing serum lipid concentrations. Very low density lipoproteins (VLDL) and high density lipoproteins (HDL) were also isolated and quantitated. HDL₂ and HDL₃ were separated by flotation velocity in the analytical ultracentrifuge and their relative weight percent determined. The mean density of LDL from 41 individuals was determined by flotation velocity at two different solvent densities. The mean density of LDL was directly proportional to the triglyceride (r=0.65) and VLDL (r=0.50) concentrations and inversely proportional to the HDL (r=−0.55) and HDL₂ (r=−0.74) concentrations (all significant at P<0.001). The mean molecular weight of LDL from 42 individuals was determined by flotation equilibrium centrifugation. The mean molecular weight of LDL was directly proportional to the HDL (r=0.49) and HDL₂ (r=0.48) concentrations and inversely proportional to the serum triglyceride (r=−0.60) and VLDL (r=−0.48) concentrations (all significant at P<0.005 except triglyceride—P<0.001). The molecular weight of LDL was inversely proportional to its density, and thus inversely proportional to its protein/lipid ratio which was confirmed by composition measurements. The density and molecular weight of LDL had no relationship to the concentration of LDL (r=0.04 and 0.03). A preliminary report of this study was given at the American Society for Biological Chemists Meeting in St. Louis, June 1981.     

Oxidative Modification and Poor Protective Activity of HDL on LDL Oxidation in Thalassemia

Oxidative modification of low-density lipoprotein (LDL) has been reported in thalassemia, which is a consequence of oxidative stress. However, the levels of oxidized high-density lipoprotein (HDL) in thalassemia have not been evaluated and it is unclear whether HDL oxidation may be linked to LDL oxidation. In this study, the levels of total cholesterol, iron, protein, conjugated diene (CD), lipid hydroperoxide (LOOH), and thiobarbituric acid reactive substances (TBARs) were determined in HDL from healthy volunteers and patients with β-thalassemia intermedia with hemoglobin E (β-thal/Hb E). The protective activity of thalassemic HDL on LDL oxidation was also investigated. The iron content of HDL₂ and HDL₃ from β-thal/HbE patients was higher while the cholesterol content was lower than those in healthy volunteers. Thalassemic HDL₂ and HDL₃ had increased levels of lipid peroxidation markers i.e., conjugated diene, LOOH, and TBARs. Thalassemic HDL had lower peroxidase activity than control HDL and was unable to protect LDL from oxidation induced by CuSO₄. Our findings highlight the oxidative modification and poor protective activity of thalassemic HDL on LDL oxidation which may contribute to cardiovascular complications in thalassemia.     

Changes in high density lipoprotein subfraction lipids during neutral lipid transfer in healthy subjects and in patients with insulin-dependent diabetes mellitus

While it is known that the transfer of cholesteryl ester (CE) from high density lipoprotein (HDL) to the apo B-containing lipoproteins is increased in patients with diabetes, the extent to which the various lipoprotein fractions engage in neutral lipid exchange and the magnitude to which triglyceride (TG) is translocated is not known. To examine in greater detail neutral lipid net mass transfer in diabetes, the HDL subfractions and the apo B-containing lipoproteins were separated, and the net mass transfer of CE and TG was compared to that of control subjects. In both groups, bidirectional transfer of CE from HDL₃ to very low density lipoprotein (VLDL) + low density lipoprotein (LDL) and of TG from VLDL+LDL to HDL₃, took place, but this process was significantly greater (P<.01) in insulin-dependent diabetes mellitus (IDDM). In contrast, CE and TG accumulated in HDL₂ to a similar degree in normal and IDDM subjects. In recombination experiments with each of the apo B-containing lipoproteins, IDDM VLDL had a greater capacity to facilitate the exchange of core lipids from both IDDM and control HDL₃: on the other hand, LDL from IDDM and control subjects both donated TG and CE to HDL₂ and affected little change in HDL₃. These findings indicate that all the major plasma fractions normally participate in the trafficking of CE and TG among the lipoproteins during neutral lipid transfer and show that the principal perturbation in cholesteryl ester transfer in IDDM involves altered interaction between VLDL and the HDL₃ subfraction.     

The effect of dietary n−3 polyunsaturated fatty acids on HDL cholesterol in Chukot residentsvs muscovites

Native Chukot Peninsula residents, in contrast to Muscovites, consume a diet rich in n−3 polyunsaturated fatty acids. This dietary peculiarity is reflected in differences in plasma lipid and apolipoprotein contents. The Chukot residents have lower contents of total cholesterol, triglyceride, LDL (low density lipoprotein) cholesterol and apolipoprotein B, but higher HDL (high density lipoprotein) cholesterol levels than do Muscovites. The apolipoprotein A-I levels were identical in both groups. A higher HDL cholesterol to apolipoprotein A-I ratio was determined in the coastline Chukot residents (0.52±0.01) than in Muscovites (0.43±0.01; p<0.01). In contrast to Muscovites, the coastline Chukot residents also had higher n−3 and lower n−6 polyunsaturated fatty acid percentages in plasma and erythrocyte lipids, and lower phosphatidylcholine and higher sphingomyelin or phosphatidylethanolamine levels in HDL_2b and HDL₃. The higher HDL cholesterol levels in the plasma of the coastline Chukot residents appears to reflect the higher cholesterol-scavenging capacity of their HDL. We conclude from this study that the regular consumption of dietary n−3 polyunsaturated fatty acids by the coastline Chukot residents decreased LDL cholesterol transfer from plasma to peripheral cells, and enhanced cholesterol efflux from cellular membranes toward HDL.     

Statin Treatment Improves Plasma Lipid Levels but not HDL Subclass Distribution in Patients Undergoing Percutaneous Coronary Intervention

Despite the established efficacy of statin therapy, the risk of cardiovascular events remains high in many patients. We examined high-density lipoprotein (HDL) subclass distribution profiles among statin-treated coronary heart disease (CHD) patients undergoing percutaneous coronary intervention (PCI). Plasma HDL subclasses were measured in 85 patients with established CHD and quantified by two-dimensional gel electrophoresis and immunoblotting. In CHD patients with statin treatment, the mean value of total cholesterol (TC) reached the desirable level and the triacylglycerol level (TAG) was borderline high. Moreover, low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), apolipoproteinA-I, and apolipoproteinB-100 levels in these patients resembled those in normolipidemic healthy subjects. The HDL subclass did not show a normal distribution and was characterized by the lower large-sized HDL_2b contents and higher contents of small-sized preβ₁-HDL in CHD patients, compared to those in normolipidemic control subjects. Multiple stepwise regression analysis revealed that the severity of coronary stenosis, determined by the Gensini Score, was significantly and independently predicted by HDL_2b and HDL_3b. Statin therapy was effective in modifying plasma lipids levels, but not adequate as a monotherapy to normalize the HDL subclass distribution phenotype of patients with CHD undergoing PCI. The HDL subclass distribution may aid in risk stratification, especially in patients with CHD and therapeutic LDL-C and HDL-C levels.     

Effects of diet and high density lipoprotein subfractions on the removal of cellular cholesterol

The effects of isocaloric substitutions of dietary polyunsaturated and saturated fat on the composition and function of plasma high density lipoproteins (HDLs) were studied in 3 normal subjects who were fed saturate-rich and polyunsaturate-rich diet programs. Compared to the saturated diets (P/S=0.4), polyunsaturated fat diets (P/S=4 or 2) reduced both plasma cholesterol and triglyceride levels. In 2 of the subjects, HDL cholesterol concentrations increased with polyunsaturated fat caused a reduction in HDL fatty acyl content of oleate and an increase in linoleate. To determine whether the altered composition affected the removal of cell membrane cholesterol, HDL and their subfractions, HDL₂ and HDL₃, which were isolated from each of the diets, were incubated with Ehrlich ascites cells in vitro. The cells were prelabeled with [³H] cholesterol, and the release of labeled cholesterol from the cells into the medium containing the various HDL fractions was determined. HDL, irrespective of the type of dietary fat, caused a release of [³H] cholesterol from the cells into the medium. The amount of [³H] cholesterol recovered in the medium was dependent on the absolute concentration of HDL cholesterol added to the cells and was independent of the type of diet. These results indicate that HDL facilitates the removal of cholesterol from cells, but that the amount and rate of removal are independent of the changes in HDL composition that can be obtained by dietary perturbations.     

Gender and age differences in the distribution of the HDL subclasses among the Chinese population

Background and aims: to analyze the gender and age differences in the distribution of the high‐density lipoprotein (HDL) subclasses among the Chinese population, and to clarify the mechanism of these changes. Methods and results: the apoA‐I contents of the plasma HDL subclasses were determined by 2‐DE coupled with immunodetection in 324 men (including 186 normolipidemic subjects) and 186 women (including 114 normolipidemic subjects). The contents of preβ₁‐HDL and HDL₃ (HDL_3c, HDL_3b, HDL_3a) were significantly lower, whereas the contents of HDL_2a and HDL_2b were higher for women than for men in the <50 years age group. Moreover, the contents of preβ₁‐HDL and HDL₃ were higher for female subjects; the HDL_2a and HDL_2b contents were lower for both female and male subjects in the 50–59, 60–69, and ≥70 years age groups versus the subjects of the same gender in the <50 years age group. When compared to the normolipidemic premenopausal women, preβ₁‐HDL, HDL_3b, and HDL_3a increased while HDL_2b decreased significantly in normolipidemic men and postmenopausal women. Conclusions: the contents of the large‐sized HDL particles HDL_2b were higher, but the contents of the small‐sized HDL particles (preβ₁‐HDL, HDL_3b, HDL_3a) were lower for women versus men in the <50 years age group. Meanwhile, the gender difference in distribution of the HDL subclass narrowed obviously with advancing age. Moreover, the characteristics of the HDL subclass distribution profile for the normolipidemic postmenopausal women resembled those for the normolipidemic men.     

The influence of plasma apolipoprotein A‐II concentrations on HDL subclass distribution

Background and aims: To investigate the impact of plasma apoA‐II concentrations on the alteration of HDL subclass distribution, and the cooperative effect of apoA‐I and apoA‐II on it. Methods and results: The apoA‐I contents of plasma HDL subclasses were quantified by two‐dimensional gel electrophoresis associated with immunodetection for 292 Chinese people. These subjects were divided according to the mean ± 1 SD of apoA‐II and apoA‐I levels as two cut‐points, respectively. Compared with the low‐apoA‐II group, the apoA‐I contents of HDL_3a (in the high group), HDL_3b, and HDL_2b increased strikingly, both in the middle‐ and high‐apoA‐II group. The apoA‐I contents of all HDL subclasses increased progressively when the apoA‐I and apoA‐II levels simultaneously or the apoA‐I/apoA‐II ratio increased, and in comparison to the low‐apoA‐I–A‐II levels group, the apoA‐I contents of HDL_2b (115%) increased more significantly than those of preβ₁‐HDL (39%) in the high‐apoA‐I–A‐II levels group. Multiple analyses also indicated that the three HDL subclasses, HDL_3a, HDL_3b and HDL_2b, were independently predicted by apoA‐II. Conclusion: Excess apoA‐II can cause the accumulation of both large‐sized HDL_2b and small‐sized HDL₃, which implies that apoA‐II plays a double role in the HDL maturation metabolism. Meanwhile, the degree of HDL_2b increased significantly relative to that of preβ₁‐HDL when apoA‐I and apoA‐II levels were elevated simultaneously, suggesting that the maturation and metabolism of HDL might be promoted and reverse cholesterol transport might be enhanced.     

Intercorrelations among plasma high density lipoprotein,obesity and triglycerides in a normal population

The interrelationships among fatness measures, plasma triglycerides and high density lipoproteins (HDL) were examined in 131 normal adult subjects: 38 men aged 27–46, 40 men aged 47–66, 29 women aged 27–46 and 24 women aged 47–66. None of the women were taking estrogens or oral contraceptive medication. The HDL concentration was subdivided into HDL_2b, HDL_2a and HDL₃ by a computerized fitting of the total schlieren pattern to reference schlieren patterns. Anthropometric measures employed included skinfolds at 3 sites, 2 weight/height indices and 2 girth measurements. A high correlation was found among the various fatness measures. These measures were negatively correlated with total HDL, reflecting the negative correlation between fatness measures and HDL₂ (as the sum of HDL_2a and_2b). Fatness measures showed no relationship to HDL₃. There was also an inverse correlation between triglyceride concentration and HDL₂. No particular fatness measure was better than any other for demonstrating the inverse correlation with HDL but multiple correlations using all of the measures of obesity improved the correlations. Partial correlations controlling for fatness did not reduce any of the significant correlations between triglycerides and HDL₂ to insignificance. The weak correlation between fatness and triglycerides was reduced to insignificance when controlled for HDL₂. Presented (in part) at the Annual Meeting of the Oil Chemists' Society in St. Louis, MO, May 1978.     

Glycosphingolipids of human plasma lipoproteins

The content and structure of glycosphingolipids (GSL) in human plasma lipoproteins were studies. The quantitative distribution of the neutral GSL(Glc-Cer, Gal-Glc-Cer, Gal-Gal-Glc-Cer, and GalNAc-Gal-Gal-Glc-Cer) and the principal ganglioside (AcNeu-Gal-Glc-Cer) within the different lipoprotein classes was similar to that of whole plasma. The total amounts (μmol glucose/100 ml plasma) of GSL in the plasma lipoproteins of three normal subjects were VLDL (very low density lipoproteins) (trace to 0.46), LDL (low density lipoproteins) (1.08–1.48), HDL₂ (high density lipoproteins₂) (0.62–0.85), and HDL₃ (high density lipoproteins₃) (trace to 0.28). In subjects with Lp(a) lipoproteins, HDL₂ rather than HDL₃ contained most of the GSL in HDL. When the data were corrected for differences in the plasma concentrations of the lipoproteins, the total amounts of GSL(nmol glucose/mg lipoprotein cholesterol) were VLDL(trace to 21.20), LDL(11.70–15.36), HDL₂(8.50–9.10), and HDL₃(3.12). No GSL were detected in lipoprotein deficient plasma. Mass spectrometry of the trimethylsilyl derivatives of the GSL in LDL showed major fragment ions characteristic of their individual structural components. The elevated plasma levels of the GSL(2–18 fold), in a homozygote for familial hypercholesterolemia, resided in LDL which contained an absolute increase (per mg lipoprotein cholesterol) of GSL. Most, if not all, of the plasma GSL are associated with plasma lipoproteins and may have an important role in their biological functions.     

Eicosapentaenoic acid is primarily responsible for hypotriglyceridemic effect of fish oil in humans

The aim of this study was to determine whether eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA), or both, were responsible for the triglyceride (TG)-lowering effects of fish oil. EPA (91% pure) and DHA (83% pure), a fish oil concentrate (FOC; 41% EPA and 23% DHA) and an olive oil (OO) placebo (all ethyl esters) were tested. A total of 49 normolipidemic subjects participated. Each subject was given placebo for 2–3 wk and one of the n-3 supplements for 3 wk in randomized, blinded trials. The target n-3 fatty acid (FA) intake was 3 g/day in all studies. Blood samples were drawn twice at the end of each supplementation phase and analyzed for lipids, lipoproteins, and phospholipid FA composition. In all groups, the phospholipid FA composition changed to reflect the n-3 FA given. On DHA supplementation, EPA levels increased to a small but significant extent, suggesting that some retroconversion may have occurred. EPA supplementation did not raise DHA levels, however, FOC and EPA produced significant decreases in both TG and very low density lipoprotein (VLDL) cholesterol (C) levels (P<0.01) and increases in low density lipoprotein (LDL) cholesterol levels (P<0.05). DHA supplementation did not affect cholesterol, triglyceride, VLDL, LDL, or high density lipoprotein (HDL) levels, but it did cause a significant increase in the HDL₂/HDL₃ cholesterol ratio. We conclude that EPA appears to be primarily responsible for TG-lowering (and LDL-C raising) effects of fish oil.     

Interaction of plasma high density lipoprotein HDL2b (d 1.063–1.100 g/ml) with single-bilayer liposomes of dimyristoylphosphatidylcholine

Incubation of a major subfraction, HDL_2b (d 1.063–1.100 g/ml), of human plasma high density lipoproteins, HDL (d 1.063–1.21 g/ml), with single-bilayer liposomes of dimyristoylphosphatidylcholine (DMPC) resulted in uptake of DMPC by the HDL_2b and dissociation of lipid-free apolipoprotein A-I (apoA-I). In the presence of excess DMPC, the dissociated apoA-I was also incorporated with DMPC into discoidal complexes. Preliminary studies with model apoA-I-DMPC complexes indicated that they also can interact with native HDL_2b with the resultant transfer of their DMPC to HDL_2b and the concomitant release of their apoA-I. After interaction of HDL_2b with DMPC liposomes, the DMPC-enriched HDL_2b product showed a lower hydrated density and a larger particle size than the control HDL_2b. The molecular properties of the lipoprotein product suggest that stabilization of the apoA-I-depleted HDL_2b probably occurred via substitution of DMPC for the apoA-I at the HDL_2b surface rather than by fusion of the apoA-I-depleted HDL_2b. The above interactions of HDL_2b with single-bilayer liposomes and discoidal complexes indicate pathways of phospholipid transfer relevant to the possible role of HDL in the metabolism of lipoprotein surface components in vivo.     

ApoA-I secretion by rabbit intestinal mucosa cell cultures

Lipid and apolipoprotein (apo) A-I concentrations in different density fractions of New Zealand White (NZW) and Watanabe (WHHL) rabbit plasma were studied. Aside from the low plasma apoA-I and high density lipoprotein (HDL) cholesterol levels in WHHL rabbits, the distribution of apoA-I was also different between the two rabbits. ApoA-I was concentrated in both the HDL₂ and HDL₃ fractions of NZW rabbits but was found primarily in the HDL₃ fraction of WHHL rabbits. ApoA-I secretion in these two rabbits was further studiedin vitro by using intestinal and hepatocyte cell cultures. ApoA-I secretion was highest from cultures of the duodenum and the proximal end of the jejunum; whereas, cell cultures of the distal end of the small intestine secreted very little apoA-I into the medium. Intestinal cell cultures from WHHL rabbits secreted less, but significant amounts of, apoA-I compared to that of NZW rabbits. ApoA-I was most concentrated in the density range of 1.12–1.21 (HDL₃) fraction in medium containing 10% fetal calf serum (FCS). Serum-free medium promoted apoA-I secretion by intestinal cell cultures that was mostly found in the d>1.21 (lipoprotein-deficient) fraction. Hepatocytes isolated from the same rabbits by collagenase perfusion secreted little apoA-I, and it was found only in the d>1.21 fraction. The addition of oleic acid into the culture medium with 10% FCS decreased the secretion of total apoA-I and HDL by intestinal cell cultures and increased the secretion of very low density lipoprotein (VLDL) and intermediate density lipoproteins (IDL). The results indicate that intestinal cells, not hepatocytes, are responsible for the secretion of apoA-I and HDL₃ in rabbits, and that the secretion may be regulated under different nutritional conditions.     

Long-Term Alcohol Consumption Caused a Significant Decrease in Serum High-Density Lipoprotein (HDL)-Cholesterol and Apolipoprotein A-I with the Atherogenic Changes of HDL in Middle-Aged Korean Women

Light-to-moderate alcohol drinking is associated with a low incidence of cardiovascular disease (CVD) via an elevation of high-density lipoproteins-cholesterol (HDL-C), particularly with the short-term supplementation of alcohol. However, there is no information on the change in the HDL qualities and functionalities between non-drinkers and mild drinkers in the long-term consumption of alcohol. This study analyzed the lipid and lipoprotein profiles of middle-aged Korean female non-drinkers, mild-drinkers, and binge-drinkers, who consumed alcohol for at least 10 years. Unexpectedly, the serum levels of HDL-C and apolipoprotein A-I (apoA-I) were decreased significantly depending on the alcohol amount; the binge-drinker group showed 18% and 13% lower HDL-C (p = 0.011) and apoA-I levels (p = 0.024), respectively, than the non-drinker group. Triglyceride (TG) and oxidized species, malondialdehyde (MDA), and low-density lipoproteins (LDL) levels were significantly elevated in the drinker groups. Interestingly, the binge-drinker group showed 1.4-fold higher (p = 0.020) cholesterol contents in HDL₂ and 1.7-fold higher (p < 0.001) TG contents in HDL₃ than those of the non-drinker group. The mild-drinker group also showed higher TG contents in HDL₃ (p = 0.032) than the non-drinker group, while cholesterol contents were similar in the HDL₃ of all groups. Transmission electron microscopy (TEM) showed that the non-drinker group showed a more distinct and clear particle shape of the LDL and HDL image with a larger particle size than the drinker group. Electrophoresis of LDL showed that the drinker group had faster electromobility with a higher smear band intensity and aggregation in the loading position than the non-drinker group. The HDL level of binge drinkers showed the lowest paraoxonase activity, the highest glycated extent, and the most smear band intensity of HDL and apoA-I, indicating that HDL quality and functionality were impaired by alcohol consumption. In conclusion, long-term alcohol consumption in middle-aged women, even in small amounts, caused a significant decrease in the serum HDL-C and apoA-I with atherogenic changes in LDL and HDL, such as an increase in TG and MDA content with a loss of paraoxonase activity.     

Effect of chronic glucagon administration on lipoprotein composition in normally fed,fasted and cholesterol-fed rats

Male adult Wistar rats received daily (at 9 a.m. and 5 p.m.) 10 μg of zinc-protamine glucagon by subcutaneous injection for 8 days. Plasma cholesterol levels were decreased by 36% in fed rats, 33% in cholesterol-fed rats and by 55% in fasted rats. Lipoproteins were separated into 22 fractions by ultracentrifugation using a density gradient. Glucagon administration decreased the cholesterol content in all lipoproteins except low density lipoprotein (LDL₁) (1.006–1.040) and very low density lipoprotein (VLDL) from cholesterol-fed rats. The main decrease (−57 to −81%) was observed in 1.050–1.100 g/mL lipoproteins (LDL₂ and HDL₂), which contained a large amount of apo E, while HDL₃ cholesterol was not affected. Triacylglycerol levels were decreased only in chylomicrons and VLDL (−70%) of fed and cholesterol-fed rats, while plasma and lipoprotein triacylglycerol levels were not changed in fasted rats treated with glucagon. In normally fed rats glucagon administration increased by 42% the fractional catabolic rate of [¹²⁵I]HDL₂ while the absolute catabolic rate appeared to be unchanged. Glucagon seems to be a potent hypolipidemic agent affecting mainly the apo E-rich lipoproteins. Its chronic administration limits lipoprotein accumulation which occurs upon cholesterol feeding.     

Plasma high density lipoprotein subgroup distribution in rats fed diets with varying amounts of sucrose and sunflower oil

The effect of varying the dietary sunflower oil/sucrose (SO/SU) ratio on rat plasma lipid concentration and lipoprotein distribution was studied. Four groups of 10 rats were fed for 4 weeks diets with varying SO/SU ratios. Lipoprotein components were then estimated in whole plasma and after cumulative density ultracentrifugation. Whole plasma triacylglycerol (TG), total cholesterol (TC) and free cholesterol (FC) decreased with increasing SO/SU ratio; the CE/FC ratio increased, because CE remained virtually unaltered. Plasma TG-lowering was due to a decrease in VLDL and LDL-TG. Protein, CE and FC in d=1.063–1.100 g/ml (HDL_2b) and d=1.100–1.125 g/ml (HDL_2a) lipoproteins decreased upon increasing the SO/SU ratio. In contrast, in d=1.125–1.200 g/ml (HDL₃) lipoproteins, there was a concomitant increase in these components. Although increasing the SO/SU ratio effected more protein and CE transportation in HDL₃ and less in HDL₂, the total amount of these components in high density lipoproteins (d=1.063–1.200 g/ml) remained constant. Apo A-I and apo C-III decreased in HDL₂ but increased in HDL₃ upon increasing the SO/SU ratio. Also, HDL₂ apo E, and the apo C-II/apo C-III and small apo B/large apo B ratios in VLDL and LDL were lowered by increasing the SO/SU ratio. The hepatic VLDL-TG output during isolated liver perfusion was lowest in rats fed the diet with the highest SO/SU ratio. In perfusate, like in plasma, the VLDL and LDL apo C-II/apo C-III ratio, as well as the small apo B/large apo B ratio, decreased upon increasing the dietary SO/SU ratio. The results indicate that there can be appreciable diet-dependent variations in plasma HDL subgroup distribution in spite of unchanged total HDL levels.     

Alterations of high density lipoprotein subclasses in obese subjects

The object of this study was to investigate the characteristics of lipid metabolism in obese subjects, with particular emphasis on the alteration of HDL subclass contents and distributions. A population of 581 Chinese individuals was divided into four groups (25 underweight subjects, 288 of desirable weight, 187 overweight, and 45 obese) according to body mass index (BMI). Apoprotein A-I (apoA-I) contents of plasma HDL subclasses were determined by 2-D gel electrophoresis associated with an immunodetection method. The concentrations of TG and the apoA-I content of pre-α₁-HDL were significantly higher (P<0.01 and P<0.01, respectively), but the levels of HDL cholesterol, and the apoA-I contents of HDL_2a and HDL_2b were significantly lower (P<0.01, P<0.05, and P<0.01, respectively) in obese subjects than in subjects having a desirable weight. Moreover, with the elevation of BMI, small-sized pre-α₁-HDL increased gradually and significantly, whereas large-sized HDL_2b decreased gradually and significantly. Meanwhile, the variations in HDL subclass distribution were more obvious with the elevation of TG levels in obese as well as overweight subjects. In addition, Pearson correlation analysis revealed that BMI and TG levels were positively correlated with pre-α₁-HDL but negatively correlated with HDL_2b. Multiple regression analysis also showed that TG concentrations were associated independently and positively with high pre-α₁-HDL and independently and negatively with low HDL_2b in obese and overweight subjects. The HDL particle size was smaller in obese and overweight subjects. The shift to smaller size was more obvious with the elevation of BMI and TG, especially TG levels. These observations, in turn, indicated that HDL maturation might be abnormal, and reverse cholesterol transport might be impaired. The first two authors contributed equally to this study.     

Effect of a salmon diet on the distribution of plasma lipoproteins and apolipoproteins in normolipidemic adult men

The effects of n−3 fatty acids on plasma lipids, lipoproteins and apoproteins have usually been studied in humans after feeding of purified fish oil. This study describes the effect of a natural diet, containing salmon as the source of n−3 fatty acids, on these parameters as compared to a diet very low in n−3 fatty acids. The subjects were nine normolipidemic, healthy males who were confined to a nutrition suite for 100 days. During the first 20 days of the study the participants were given a stabilization diet consisting of 55% carbohydrates, 15% protein, and 30% fat. The n−3 content of this diet was less than 1%, and it contained no 20- or 22-carbon n−3 fatty acids. After the stabilization period the men were split into two groups, one group continued on the stabilization diet while the other received the salmon diet that contained approximately 2.1 energy percent (En%) of calories from 20- and 22-carbon n−3 fatty acids. Both diets contained equal amounts of n−6 fatty acids. This regime continued for 40 days, then the two groups switched diets for the remainder of the study. Plasma triglycerides were lowered significantly (p<0.01) and high density lipoprotein cholesterol (HDL-C) was significantly elevated (p<0.01) after the men consumed the salmon diet for 40 days. The very low density lipoproteins (VLDL) were lowered, but the trend did not reach statistical significance during the intervention period. The total plasma cholesterol, total low density lipoprotein (LDL) and the total high density lipoprotein (HDL) levels were not influenced by the salmon diet. Within the HDL fraction, however, the larger HDL₂ subfractions were significantly elevated (p<0.002), and the smaller, more dense HDL₃ was lowered (p<0.002) by the salmon diet. These significant changes were detected by analytic ultracentrifugation and confirmed by gradient gel electrophoresis. Analysis of the apolipoproteins (apo) AI, AII, B, and E, and Lp(a) indicated only significant lowering of apoAI, consistent with the increased HDL₂, which is higher in cholesterol but lower in the major HDL apolipoprotein, apoAI. Thus, the purported beneficial cardiovascular effects of consumption of n−3 fatty acids by humans may, in part, be attributable to changes in the HDL distribution,i.e., the lowering of the more dense HDL₃ and the elevation of the larger, less dense HDL₂.